The present invention relates to a process for recovering valuable metals such as zinc, iron and the like from a dust having a higher content of zinc, such as the one generated in an electric arc furnace for steel manufacture or the like.
A dust generated in an iron and/or steel melting furnace, such as the electric arc one, is thus far collected by means of a dust collector. The amount of the dust generated normally corresponds to 1 to 1.5% by weight of the crude steel manufactured, and the dust contains large amounts of valuable metals, namely 25 to 30% by weight of iron, 20 to 25% by weight of zinc and 3 to 4% by weight of lead. The present situation is, however, such that the dust is to be subjected to a collective treatment by specific refiners to whom the dust generated is handed over, due to unavailability of a proper and easy recovering method of the valuable metals which can be operated on a simple and small scale.
Several methods have been proposed as the recovering method, including a rotary kiln method and also recently, a treating method using plasma heat.
The former method aims mainly at separating zinc from other materials in the dust and comprises reducing the zinc and iron oxide in the dust by means of a rotary kiln and separating the resulting metals. This method, however, has the drawbacks of the complexity of process and a high energy consumption; that is, since the free board atmosphere in the rotary kiln is highly oxidizing, the zinc vapor once reduced and separated is reoxidized in the free board of the rotary kiln, so that it must be further processed in a zinc smelting furnace, electrowinning or the like, to be recovered as metallic zinc. Further, the reduction product of the iron component thus obtained is a sponge iron containing a large amount of gangue minerals, so that it cannot be recovered and used as is as useful resources and hence has not yet been recovered as metallic iron.
In the latter method, since a large amount of energy is consumed for plasma generation, and the zinc and iron recovered are of relatively low value considering the energy consumed, no satisfactory result has been obtained which justifies the cost of treatment.
Moreover, another problem involved in the method is that the excessively high temperature used in the method causes the vaporization of undesirable metals, e.g., copper and resultant contamination of the zinc product.
The present invention has been achieved in view of such circumstances. The object of the invention is to provide a process for recovering valuable metals from an iron dust containing zinc easily and with a low energy consumption for treatment.